This section introduces aspects that may facilitate a better understanding of the invention(s). Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
In Long-Term Evolution (LTE), there are various physical channels. An uplink physical channel corresponds to a set of resource elements carrying information originating from higher layers. The following uplink physical channels are defined: Physical Uplink Shared Channel (PUSCH); Physical Uplink Control Channel (PUCCH); and Physical Random Access Channel (PRACH).
Physical random access channel (PRACH) in uplink is a very important physical channel. All user equipments (UEs) start random access into a cell only by PRACH, using different format and resource configured by the cell. Only after successful access, the UE can establish the radio bearer (RB) and transmit user data in uplink and receive data in downlink.
In Reference 1, 3GPP TS 36.211 v8.6.0, “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation”, time and frequency structure of PRACH has been described. The physical layer random access preamble consists of a cyclic prefix of length TCP and a sequence part of length TSEQ. According to the LTE standard, there are five types of PRACH format. Each type occupies 6 resource blocks (RBs) in frequency. During a same period of time, there maybe have several PRACH resources with a same format. They occupy different positions in frequency.
For example, FIG. 1 illustrates an example of resource allocation wherein two PRACH resources with the same format 0 exist in a same sub-frame.
FIG. 1 shows the operating bandwidth and one sub-frame consisted of two time slots. The PUCCH resources typically consist of number of resource blocks, at edge of the operating bandwidth. The PUCCH supports multiple formats: format 1, format 1a, format 1b, format 2, format 2a, and format 2b. In the below, the multiple formats are abbreviated as PUCCH1/1a/1b, PUCCH2/2a/2b, respectively. The middle part is PUSCH resources. Two PRACH resources are located within the PUSCH resources.
As seen from FIG. 1, the PUSCH resources are divided into three separate islands by the two PRACH resources and cannot be completely used due to Single Carrier rule in LTE uplink. In LTE, Single Carrier rule requires that the PUSCH resource allocated for a UE must be continuous on frequency in one slot.
A discontinuous PUSCH resource will result in low resource usage efficiency in all cases. For example, FIG. 2 shows the PUSCH allocation for one UE in the single UE case. The allocation of PUCCH and PRACH is similar with that shown in FIG. 1. The middle segment (part 2) of the PUSCH resources is allocated for the single UE 1. The upper segment (part 1) and the lower segment (part 3) of the PUSCH resources cannot be allocated to UE 1 to use. It can be seen that the single UE cannot fully utilize all the PUSCH resource, causing the uplink throughput unable to reach the peak rate.
In the multiple UEs case, if one UE need more frequency resource (i.e., resource blocks) than the PUSCH fragment (e.g., part 1 and part 3 as shown in FIG. 1) to transmit the uplink data, then it has to allocate resource from a larger PUSCH segment (e.g., part 2 as shown in FIG. 1) and leave those PUSCH frequency resources (i.e., RBs) between the PUCCH and the PRACH unused even if they are free to use. On the other hand, if one UE need fewer RBs than the PUSCH fragment, although the fragment can be used to allocate resources for that UE, it still will leave a smaller fragment unused after consuming some part of the fragment.
3GPP standard also provides the flexibility of configuring PRACH at different position within the frequency spectrum. In this regard, it is possible to move PRACH form PUSCH into PUCCH area to achieve continuous PUSCH resource block. Unfortunately, it may still meet trouble in odd number PRACH case as illustrated in FIG. 3.
FIG. 3 shows the PRB “hole” in the PUCCH area when the PRACH number is odd. As shown in FIG. 3, existing PUCCH layout is a symmetric structure to support frequency hopping, so PRACH also must reserve two symmetric parts located at two ends of the frequency spectrum. The SR1 and SR2 in FIG. 3 are the parts for PUCCH format 1. However, if the PRACH number is odd, how to utilize the other one (?? part shown in FIG. 3)? Due that the PRACH cannot support frequency hopping, that idle part cannot be used by PUCCH. Otherwise, the second slot of PUCCH will conflict with PRACH. The only feasible usage is for PUSCH. However, it will still result in the discontinuous PUSCH resource like shown in FIGS. 1-2.